1. Field of the Invention
This invention relates to an internal combustion engine, and more particularly to an engine including a mechanical supercharger connected to a crankshaft via a clutch and selectively turned ON or OFF by controlling the clutch.
2. Description of the Related Art
A mechanical supercharger is usually connected to an engine crankshaft via a solenoid clutch, which is controlled to be engaged (turned ON) or disengaged (turned OFF) in accordance with the engine load. Consequently, when the engine is running in a high load condition, the solenoid clutch is turned ON to operate the mechanical supercharger to supplement the air intake. On the other hand, when the engine is running in a low load condition, the solenoid clutch is turned OFF to stop the supercharger and cut off the supplementary air intake.
Thus, in an internal combustion engine including a mechanical supercharger which is turned ON by engaging a solenoid clutch when the engine load (or the opening degree of a throttle valve) is higher than a predetermined value, an improved supercharger has been already proposed in Japanese Utility Model Application No. 59-140365 filed by the applicant (assignee) of this application, in which, when this supercharger is changed from an OFF to an ON condition, the solenoid clutch is periodically controlled so as to prevent an abrupt change in engine torque, unfavorable drivability, and wheel spin.
However, in the mechanical supercharger disclosed in the above-mentioned prior application, the clutch means is subjected to repeated friction, since it is periodically controlled whenever it is changed from an OFF to an ON condition. Therefore, the clutch elements of this supercharger must be made of an endurable and wear-resistant material.